The present invention relates to a semiconductor device and particularly concerns an integrated circuit (hereinafter, referred to as an IC) having a function of temperature compensation to be used in combination with a variety of sensors, and a sensor IC combining a sensor with the IC having the temperature compensation function.
Conventionally, a sensor IC, which combines a sensor and an IC for processing a signal, has been used in a variety of fields. As a sensor IC with the function of turning on/off in response to an output signal of a sensor, a sensor IC for detecting magnetic fields has been particularly known. For example, a magnetic sensor IC is used for detecting rotation of a cooling fan for a CPU of a personal computer and so on.
Incidentally, in case of an IC which operates amplification on an output signal (electric signal) from the sensor and turns on/off the output at predetermined sensitivity, the output from the sensor normally changes with temperature. Thus, a temperature-compensating circuit is necessary for turning on/off the output of the IC at predetermined sensitivity all the time regardless of temperature. As temperature compensation, a conventional method has been known which changes an amplification degree of an output signal or voltage and current applied to the sensor according to a temperature characteristic of the output signal from the sensor.
For example, according to the invention disclosed in Japanese Patent Laid-Open No. 57-197883, temperature compensation is performed by applying to a sensor voltage increasing monotonously with temperature and driving the sensor by the voltage. However, some sensors require an extremely high voltage for driving, thereby increasing power consumption or heat generation. Consequently, the operation becomes unstable with temperature.
Further, the invention disclosed in Japanese Patent Publication No. 3-51118 has been known. The invention is provided with a Hall element (sensor) for generating Hall voltage, a reference voltage generating means for generating reference voltage relative to current passing through the Hall element, a comparing means for generating an output signal depending upon a relative magnitude of the Hall voltage and the reference voltage, and so on. Temperature compensation can be performed on a variety of sensors having sensitivity as a function of applied current.
As described above, the invention described in Japanese Patent Publication No. 3-51118 is applicable to a sensor where sensitivity is a function of applied current. However, the invention is not applicable to a sensor where sensitivity has no correlation to applied current. Moreover, the temperature-compensating circuit is not for general purpose use and cannot be combined with other sensors, resulting in narrow applicability.
Additionally, even in the case where a sensor is formed in the same manner, the same current is not always applied at the same sensitivity. Conversely, the same sensitivity is not always obtained at the same current. Therefore, in case of a large irregularity in characteristic of the sensor, monitoring current may be an adverse effect.
Incidentally, in the temperature-compensating circuit formed on widely used bulk silicon, leakage current rapidly increases on a PN-junction at a high temperature of 125xc2x0 C. or above, causing a problem in temperature compensation. Temperature compensation is not possible particularly at a high temperature of 150xc2x0 C. or above.
Meanwhile, as a technique for a high-temperature IC, a method has been known, which forms circuits on a semiconductor layer on an insulating base such as an SOI (silicon on insulator) substrate. It has been known that this method makes it possible to reduce an area of a PN-junction, reduce leakage current in a high temperature range, prevent a latch-up phenomenon, and permits an operation at a higher temperature. Hence, if the temperature-compensating circuit according to the conventional method is formed on the semiconductor layer on the SOI substrate, it is expected to somewhat improve the operation at a high temperature.
However, in the case where the temperature-compensating circuit of the conventional method is formed on the semiconductor layer on the SOI substrate, it is difficult to achieve accurate temperature compensation with reliability at a high temperature, and durability is deteriorated at a high temperature due to heat generated by power consumption.
In order to solve the above problem, it is necessary to accurately amplify a fine signal from the sensor and to perform accurate temperature compensation with a low driving voltage and small power consumption at a high temperature. However, it is not easy to realize a sensor IC meeting these conditions.
Hence, a sensor IC combining a sensor and an IC with temperature compensation, that accurately operates in a stable manner at a high temperature of 200xc2x0 C. or above, has not been achieved yet. Also, the IC for temperature compensation for the sensor IC has not been achieved. Such a sensor IC has been demanded.
Further, as a detector for rotation of a gear wheel, a silicon-monolithic sensor IC using a CMOS circuit has been known. However, the highest temperature of the sensor IC is limited to 150xc2x0 C. in practical use. It has been desirable to set the highest temperature at 200xc2x0 C. or above.
The present invention is therefore devised against the above backdrop. The first object thereof is to provide a semiconductor device as an IC with temperature compensation (hereinafter, referred to as an IC for a sensor IC) that combination can be made with various sensors and can perform accurate temperature compensation on an output signal from the sensor with reliability at a high temperature.
The second object of the present invention is to provide a semiconductor device as a sensor IC (hereinafter, referred to as a sensor IC) that can accurately operate with reliability in a stable manner at a high temperature.
The present invention provides a semiconductor device (IC for a sensor IC) including amplifying means for inputting a sensor output signal from the sensor, amplifying the sensor output signal at a required temperature-independent amplification factor, and canceling an offset, reference signal producing means for producing a reference signal varying at a temperature coefficient equal to that of the sensor output signal from the sensor, comparing means which compares the magnitude of an amplification output signal from the amplifying means with that of the reference signal from the reference signal producing means and outputs a required signal according to a comparison result, and constant voltage generating means for generating temperature-independent constant voltage to be supplied to the sensor, characterized in that the amplifying means, the reference signal producing means, the comparing means, and the constant voltage generating means are formed using a semiconductor layer provided on an insulating substrate.
Here, the above xe2x80x9cequal temperature coefficientxe2x80x9d includes not only an equal temperature coefficient but also a substantially equal temperature coefficient. A permissible error value depends upon the accuracy of the semiconductor device (sensor IC).
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable, in which the semiconductor layer is composed of a silicon thin film.
Further, as an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable, in which the silicon thin film is 30 nm to 1000 nm in thickness.
As described above, according to the IC for the sensor IC, the amplifying means receives a sensor output signal, amplifies the sensor output signal at a required temperature-independent amplification factor, and operates to cancel an offset, thereby accurately amplifying the sensor output signal.
Furthermore, the reference signal producing means produces a reference signal varying at a temperature coefficient equal to that of the sensor output signal of the sensor. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Even when the output signal of the sensor is affected by temperature, the influence can be cancelled.
Additionally, the amplifying means, the reference signal producing means, the comparing means, and the constant voltage generating means are formed using the semiconductor layer provided on the insulating substrate, the semiconductor layer is preferably composed of a silicon thin film, and leakage current is reduced in a high temperature range and latch-up can be prevented.
For this reason, according to the IC for the sensor IC of the present invention, when one of the sensors changes the outputs at a temperature coefficient equal to that of the reference signal produced by the reference signal producing means, combination can be made with the sensor. In this case, accurate temperature compensation is performed for the output of the sensor over a wide temperature range from a low temperature to a high temperature (e.g., from xe2x88x9240xc2x0 C. to 200xc2x0 C. or above), achieving an accurate operation with reliability even at a high temperature.
Furthermore, in case of forming the sensor IC combined with the sensor, the IC for sensor IC of the present invention can be realized only by changing the components of the reference signal producing means according to a temperature characteristic of the sensor. Thus, combination can be made with a variety of sensors, achieving wide applicability.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the reference signal producing means is based on the previous measurement of a temperature coefficient of the sensor output signal of the sensor and produces a reference signal having an equal temperature coefficient.
According to the embodiment, the reference signal producing means previously measures a temperature coefficient of the sensor output signal of the sensor and produces a reference signal having an equal temperature coefficient. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Thus, in case of forming the sensor IC with the combination of the sensor, accuracy of comparison is improved.
Further, the sensor can be severely selected for each characteristic upon manufacturing and assembling and the reference signal producing means can produce a reference signal according to the selected characteristic of the sensor. Thus, it is possible to readily realize a sensor IC having a desired specification by making combination with the sensor.
As an embodiment of the IC for the sensor IC of the present invention, an IC for the sensor IC is applicable in which the reference signal producing means has a temperature coefficient equal to that of the sensor output signal of the sensor and produces a reference signal changing linearly with absolute temperature.
According to the embodiment, the reference signal producing means has a temperature coefficient equal to that of the sensor output signal of the sensor and produces a reference signal changing linearly with absolute temperature. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal.
Therefore, in the embodiment, when one of the sensors has the output changing linearly with absolute temperature, a reference signal provided by a linear function of absolute temperature is produced according to the sensor, achieving the combination with the sensor. In this case, accurate temperature compensation is realized for the output of the sensor over a wide temperature range from a low temperature to a high temperature, achieving an accurate operation with reliability even at a high temperature. Moreover, even in a wide temperature range whose output is not a linear function but is approximate to a linear function, an accurate operation is possible.
As an embodiment of the IC for the sensor IC of the present invention, a sensor for a sensor IC is applicable in which the amplifying means includes a signal amplifying means which is composed of a plurality of operational amplifiers and amplifies the sensor output signal at a temperature-independent amplification factor and an offset compensating means for compensating for each offset of the plurality of the operational amplifiers every predetermined period.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the operational amplifier includes a differential amplifying section for performing differential amplification on the sensor output signal and an offset compensating section for canceling an offset voltage of the differential amplifying section, the offset compensating section receives an offset compensating signal according to an offset voltage of the differential amplifying section every predetermined period and cancels the offset voltage of the differential amplifying section in response to the offset compensation signal.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the offset compensation section further includes a capacitor for holding voltage to cancel the offset voltage of the differential amplifying section, the capacitor periodically holds a voltage according to the offset voltage of the differential amplifying section, and the offset compensating section cancels the offset voltage of the differential amplifying section according to the held voltage.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the comparing means compares the magnitude of the amplification output signal from the amplifying means with the magnitudes of two reference voltages, and the output is turned on/off according to a comparison result.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the comparing means computes a ratio of a reference voltage and the magnitude of the amplification output signal from the amplifying means and outputs a digital signal according to the ratio.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the reference signal producing means includes at least a constant voltage source for generating temperature-independent constant voltage and a constant current source for generating constant current being directly proportional to absolute temperature and inversely proportional to the resistance of a reference resistor, and the reference signal producing means produces two reference voltages changing linearly with absolute temperature, by utilizing the constant voltage generated in the constant voltage source and the constant current generated in the constant current source.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the reference signal producing means is constituted by a first constant current source for generating a constant current being directly proportional to absolute temperature and inversely proportional to the resistance of the reference resistor, a second constant current source which is connected in series to the first constant current source and applies temperature-independent constant voltage to a voltage/current converting resistor to generate constant current, a third constant current source for generating constant current being fixed times larger than a difference between a current of the second constant current source and a current of the first constant current source, and an upper limit reference voltage generating resistor and a lower limit reference voltage generating resistor which are connected in series to the third constant current source and are applied constant current from the third constant current source, and one or both of potentials generated in the upper limit reference voltage generating resistor and the lower limit reference voltage generating resistor are taken out as reference potentials.
As an embodiment of the IC for the sensor IC of the present invention, an IC for a sensor IC is applicable in which the reference resistor, the voltage/current converting resistor, the upper limit reference voltage generating resistor, and the lower limit reference voltage generating resistor are equal to one another in temperature coefficient.
Meanwhile, the present invention provides a semiconductor device (sensor IC) including a sensor for converting a measured physical quantity to an electric signal and outputting the signal, the outputted signal having a peculiar temperature coefficient, an amplifying means which inputs a sensor output signal of the sensor, amplifies the sensor output signal at a required amplification factor of temperature independence, and cancels an offset, a reference signal producing means for producing a reference signal varying at a temperature coefficient equal to that of the sensor output signal of the sensor, a comparing means for comparing the magnitude of the amplification output signal from the amplifying means with the magnitude of the reference signal from the reference signal producing means and for outputting a required signal according to a comparison result, and a constant voltage generating means for generating temperature-independent constant voltage to be supplied to the sensor, characterized in that the amplifying means, the reference signal producing means, the comparing means, and the constant voltage generating means are formed using a semiconductor layer provided on an insulating substrate.
As an embodiment of the sensor IC of the present invention, an sensor IC is applicable in which the semiconductor layer is composed of a silicon thin film.
Additionally, as an embodiment of the sensor IC of the present invention, an sensor IC is applicable in which the silicon thin film is 30 nm to 1000 nm in thickness.
As described above, according to the sensor IC of the present invention, the amplifying means inputs a sensor output signal of the sensor, amplifies the sensor output signal at a required amplification factor of temperature independence, and cancels an offset, thereby accurately amplifying the output signal of the sensor.
Further, the reference signal producing means produces a reference signal changing at a temperature coefficient equal to that of the sensor output signal of the sensor. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Hence, even when the output signal of the sensor is changed due to the influence of temperature, the influence can be cancelled.
Moreover, the amplifying means, the reference signal producing means, the comparing means, and the constant voltage producing means are formed by using a semiconductor layer provided on an insulating substrate. The semiconductor layer is preferably composed of a silicon thin film, and leakage current can be reduced in a high temperature range and latch-up can be prevented.
For this reason, according to the sensor IC of the present invention, over a wide temperature range from a low temperature to a high temperature (e.g., from xe2x88x9240xc2x0 C. to 200xc2x0 C. or above), temperature compensation can be performed accurately for the output of the sensor, achieving an accurate operation with reliability even at a high temperature.
As mentioned above, according to the sensor IC of the present invention, the reference signal producing means produces a reference signal changing at a temperature coefficient equal to that of the sensor output signal of the sensor. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Furthermore, the amplifying means amplifies the sensor output signal from the sensor at a required amplification factor of temperature independence and cancels an offset. Hence, the sensor IC of the present invention can perform accurate temperature compensation on the output of the sensor over a wide temperature range from a low temperature and a high temperature, thereby achieving an accurate operation with reliability even at a high temperature.
As an embodiment of the sensor IC of the present invention, an sensor IC is applicable in which a sensor output signal has a peculiar temperature coefficient in the sensor and the sensor output signal is produced in a linear function of absolute temperature.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the sensor is a magnetic sensor.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the magnetic sensor is a Hall element.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the Hall element has a magnetic sensitive part made of GaAs.
The invention of the embodiment is completed by the inventor et al. who considered a characteristic of GaAs having a resistance increasing with temperature and earnestly studied the characteristic for positive and effective use.
Therefore, in the present invention, GaAs is adopted for the magnetic sensitive part of the Hall element. A resistance of GaAs increases with temperature. Thus, it is possible to reduce current of the magnetic sensitive part and to reduce source current with temperature. Hence, the sensor IC decreases in power consumption at a higher temperature and it is possible to suppress an increase in temperature caused by consumption of current, thereby operating in a stable manner even at a high temperature.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the reference signal producing means previously measures a temperature coefficient of the sensor output signal of the sensor and produces a reference signal having an equal temperature coefficient.
According to the embodiment, the reference signal producing means previously measures a temperature coefficient of the sensor output signal of the sensor and produces a reference signal having an equal temperature coefficient. The signal is used as a reference, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Consequently, accuracy of comparison is improved.
Also, the sensor can be severely selected for each characteristic in manufacturing and assembling and the reference signal producing means can produce a reference signal according to the selected characteristic of the sensor. Thus, it is possible to readily realize a sensor IC having a desired specification by making combination with the sensor.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the reference signal producing means produces a reference signal having a temperature coefficient equal to that of the sensor output signal and changing linearly with absolute temperature.
According to the embodiment, the reference signal producing means produces a reference signal having a temperature coefficient equal to that of the sensor output signal of the sensor and changing linearly with absolute temperature. The signal is used as a reference signal, that of which the comparing means makes comparison with the magnitude of the amplification output signal of the amplifying means and outputs a required signal. Thus, even when the output signal of the sensor is changed due to the influence of temperature, the influence can be cancelled.
For this reason, accurate temperature compensation is possible for the output of the sensor over a wide temperature range from a low temperature to a high temperature, achieving an accurate operation with reliability even at a high temperature. Further, even in a wide temperature range whose output is not a linear function but is close to a linear function in some temperature range, an accurate operation can be realized in that temperature range.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the amplifying means is composed of a plurality of operational amplifiers and includes a signal amplifying means for amplifying the sensor output signal at a temperature-independent amplification factor and an offset compensating means for compensating for each offset of the plurality of the operational amplifiers every predetermined period.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the operational amplifier includes a differential amplifying section for performing differential amplification on the sensor output signal and an offset compensating section for canceling an offset voltage of the differential amplifying section, the offset compensating section receives an offset compensating signal according to an offset voltage of the differential amplifying section every predetermined period, and the offset voltage of the differential amplifying section is cancelled in response to the offset compensation signal.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the offset compensation section further includes a capacitor for holding voltage for canceling the offset voltage of the differential amplifying section, the capacitor periodically holds a voltage according to the offset voltage of the differential amplifying section, an the offset compensating section cancels the offset voltage of the differential amplifying section according to the held voltage.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the comparing means compares the magnitude of the amplification output signal from the amplifying means with the magnitudes of two reference voltages, and the output is turned on/off according to a comparison result.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the comparing means computes a ratio of a reference voltage and the magnitude of the amplification output signal from the amplifying means and outputs a digital signal according to the ratio.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the reference signal producing means includes at least a constant voltage source for generating temperature-independent constant voltage and a constant current source for generating constant current being directly proportional to absolute temperature and inversely proportional to the resistance of a reference resistor, and the reference signal producing means produces two reference voltages changing linearly with absolute temperature, by utilizing to the constant voltage generated in the constant voltage source and the constant current generated in the constant current source.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the reference signal producing means is constituted by a first constant current source for generating a constant current being directly proportional to absolute temperature and inversely proportional to the magnitude of the reference resistor, a second constant current source being connected in series to the first constant current source and applying temperature-independent constant voltage to a voltage/current converting resistor to generate constant current, a third constant current source for generating constant current being constant-times larger than a difference between a current of the second constant current source and a current of the first constant current source, and an upper limit reference voltage generating resistor and a lower limit reference voltage generating resistor being connected in series to the third constant current source and being applied constant current from the third constant current source, and one or both of potentials generated in the upper limit reference voltage generating resistor and the lower limit reference voltage generating resistor are taken out as reference potentials.
As an embodiment of the sensor IC of the present invention, a sensor IC is applicable in which the reference resistor, the voltage/current converting resistor, the upper limit reference voltage generating resistor, and the lower limit reference voltage generating resistor are equal to one another in temperature coefficient.